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URL Shortener

In short

It sounds like a weekend toy, but a good URL shortener touches ID generation, redirects, caching and analytics. Interviewers love asking about it, so building one gives you real stories to tell.

A production version of the classic system-design project — short code generation, redirect handling, and click analytics — a compact but genuinely impressive portfolio piece.

The purple blob swaps a very long paper scroll for a tiny paper tag.

Think of it like this

A PNR for a long train trip

Your train booking has a long list of details: train, coach, berth, date, passengers. But you only need a 10-digit PNR to pull it all up. A short link is the same: a tiny code that stands for a very long URL.

Watch it happen

Create a link, then click it

Browser

API

Redis

Postgres

POST /shorten

1/7The user sends a long URL. The API validates it is a real http or https link.

The big ideas

What you need to know

Short code generation

Base62-encode a database ID, or generate random codes and retry on collision. Know the trade-offs of each.

Fast redirects

The redirect path must be tiny: cache lookup, then 302. Everything else, like analytics, happens after.

Click analytics

Count clicks per link per day. Push click events to a queue so redirects never wait on writes.

Abuse protection

Validate URLs, rate-limit creation and allow links to be disabled, because spammers love shorteners.

See it in code

Walk through the code

1const ALPHABET = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";2 3function toBase62(id: number): string {4  let code = "";5  do {6    code = ALPHABET[id % 62] + code;7    id = Math.floor(id / 62);8  } while (id > 0);9  return code;10}11 12app.get("/:code", async (req, res) => {13  const url = (await redis.get(`url:${req.params.code}`)) ?? (await findInDb(req.params.code));14  if (!url) return res.status(404).send("Link not found");15  res.redirect(302, url); // 302 so every click reaches us and can be counted16});